If you cast a spell “without paying its mana cost,” you can’t choose to cast it for any alternative costs. You can, however, pay additional costs. If the card has any mandatory additional costs, you must pay those to cast the spell.

While you control Codie (as much as anyone can really “control” Codie), you may cast any face of a modal double-faced card that’s an instant or sorcery face, even if the other face is a permanent face.

You exile the cards face up. All players will be able to see them.

If the card has in its mana cost, you must choose 0 as the value of X when casting it without paying its mana cost.

A permanent spell is an artifact, creature, enchantment, or planeswalker spell. You may still play lands and cast instant and sorcery spells. Other effects can still put permanents onto the battlefield.

The types and mana value of a double-faced card in exile are determined by the characteristics of its front face. The mana value of a split card is the total mana value of both halves of the split card added together.

Codie’s activated ability is a mana ability. It can’t be countered or responded to, and you can activate it while casting a spell. If you do, that spell is “the next spell” you cast this turn.

The delayed triggered ability created by Codie’s second ability will resolve before the spell that caused it to trigger. That ability will resolve even if the spell is countered or otherwise doesn’t resolve.

If you exile your entire library without exiling an instant or sorcery card with a lesser mana value, you will randomize the exiled cards and they again become your library, ending the effect. You will not continue to exile and shuffle your library forever.

The mana value of the spell that caused the ability to trigger is determined only by its mana cost, no matter what the total cost to cast the spell was.

The last card exiled is not cast immediately. You may cast it until the end of the current turn. If you do not cast it, that card will remain in exile.